In a statement, the franchisor said the offer is part of an effort to give teenagers a chance to improve their mental and physical health.
The program, dubbed High School Summer Pass, runs from May 16 through August 31.
Planet Fitness launched a similar program three years ago and saw more than 900,000 teens sign up and complete more than 5.5 million workouts over a three-and-a-half-month period, the company said in a news release.
Starting Tuesday, high schoolers can pre-register on the company's website for a reminder.
"As the leader in fitness, we believe we have a responsibility to provide a welcoming, safe, and Judgement Free environment for high school students to improve their physical and mental wellness, particularly given the challenges they have and continue to face in the wake of the pandemic," Planet Fitness CEO Chris Rondeau said in a statement. "Our study found that nearly all (92 percent) high school students agreed that when they are regularly physically active, they feel much better mentally."